Process of producing variegated pressed fiberboard



July 2, 1946. H. K. uNzi-zLL PROCESS OF PRODUCING VARIEGATED PRESSEDFIBERBOARD Filed July 11, 1942 PROCESS OF PRODU PRESSED F CINGVARIEGATED ERBOARD K. Linzell, Long Lake, 111., assignor to UnitedStates Gypsum ,Qompany, Chicago, 111., a corporation of IllinoisApplication July 11, 1942, Serial No. 450,643

3 Claims. (CL 92-38) This invention relates to fiber board, and moreparticularly to a board which may be produced by the compaction ofvegetable fibers at elevated temperatures.

The production of dense fibrous products from vegetable fibers bycompaction at high temperatures is wellknown in the art. The process hasrecently been applied particularly to the production of hard pressedboard having a density in general somewhat greater than the originalmaterial from which the product is formed. In order to produce a hardfibrous product of this character, without the use of substantialamounts of binding agents, from vegetable fibers and particularly woodfibers, pressures upwards of 500 pounds per square inch and temperaturesupwards of 400 F. are required in order that a product ofthe desireddensity and strength be produced. It has been found, however, that atsuch high temperatures and pressures the vegetable material becomescolored or browned to a greater or less degree, depending upon .thedegree of temperature and pressure employed and upon the type of,vegetable material being subjected to such treatment. Thus, when a harddense board is produced from cottonwood fibers and when the fibrousmaterial is subjected to a pressure of about 2500 pounds per square inchand to a temperature of about 420 F. for'a period of about 5,

to 10 minutes, the resulting product may become browned or colored to amarked extent. This browning lends a pleasing appearance to theresuiting board and for this reason has been found to be quitedesirable.

A dense fiber board that is produced by the general method indicatedabove usually presents, when completed, a uniformly colored surface. Itis desirable, however, to produce textured fiber boards which presentvariegated surfaces without the necessity of applying paints orvarnishes to produce the desired effect. Boards having such surfaces areoften more readily salable than plain uniformly colored products,particularly if the board is to be used in interior decorative work.

It has been found that, if certain color-inducing chemicals such assalts are incorporated into thefiber board prior to the pressingoperation, the coloration due to the heat and temperature may bemarkedly increased in certain instances; and it has been further foundthat, if the concentration of such salts be localized on the surface ofdifferent portions of the board prior to the pressing. increasedcoloration will occur during the pressing in those portions of thesurface wherein the salt is most concentrated.

, A further object of this invention is to provide a method for theproduction of fiber board whose surface color may be regulated to someextent by incorporating certain catalytic color-inducing chemicals intothe fibrous material prior to the pressing operation.

A further object of this invention is to provide a fiber board with avariegated surface by varying the concentration of color-inducingchemicals which tend to increase the coloration of the fibers on thesurfaces of the board.

A further object of this invention is to provide means for concentratingthe said color-inducing chemicals in various portions of the fibrousmaterial preliminary to pressing.

Further and additional objects will appear from the followingdescription and the appended claims.

As has been previously mentioned, it has been found that certain saltsand other materials incorporated into fibrous products preliminary toheating and pressing cause an increased tendency of the fibers to becomecolorized. Suitable colorinducing chemicals have been found to beammonium carbonate, aluminum sulfate, calcium carbonate, calciumphosphate, ferric chloride, and the like. If these color-inducingchemicals are incorporated with or added to a fibrous board or sheetpreliminary to the hot pressing treatment, it will be found that thedegree of browning or coloration due to the carbonization of the fibersor the polymerization of the resinous material in the product will ingeneral be roughly proportional to the concentration of the chemicalpresent. In general, the present invention contemplates the localizationof the chemical in the material to be pressed in order that the surfaceof the resulting. product will be colorized to different degrees,although uniform heat and pressure are employed during the compaction ofthe product. The distribution of the chemical throughout or over thematerial to be pressed may be effected in avariety of ways. The chemicalmay be sprinkled in varying amounts on the surface of the productpreliminary to pressing either in the dry or wet form. This has been Thechemical may then become concentrated on.

or near the surface of the fibrous mat during the drying thereof, sincethe soluble chemical'has a 3 tendency to migrate through the fibrousproduct to the surface when the fibrous product is being dried. Whensoluble chemicals are employed, such as ammonium carbonate, oxalic acid,or ferric sulfate, they may bemore or less uniformly distributed througha wet fibrous product into which theyhave been incorporated. When thefibrous product is dried preliminary to the heating and pressingtreatment, the soluble chemical will tend to migrate to the surface withthe water that is b ing evaporated and to precipitate adjacent saidsurface. The migrating chemical may be localized or concentrated onvarious portions of the surface of the drying product by increasing therateof evaporation from the various surface areas of the fibrousmaterial. This may be effectively accomplished by the production ofraised portions or wick-like structures on the wet material, withsubsequentdrying of the same. The water evaporates more rapidly fromthose areas which have the greatest surface exregion of the surfacewhere the concentration of the chemical was the greatest.

Referring now to the drawing, Fig. 1 is a diagrammatic representation ofapparatus that may be employed for the preparation of a product inaccordance with this invention;

Fig. 2 is a plan view of a section of an unpressed board having raisedsurface portions after having passed through an embossing roll;

Fig. 3 is a section of the unpressed board taken alongv line 3'3' ofFig. 2;

Fig. 4 is a section of an unpressed board having wick-like structurespulled up from the surface of the board;

Fig. 5 is a diagrammatic sectional view of an apparatus suitable forproducing the embossings on the fibrous material of this. invention,.preliminary to the pressing, and wherein is indicated the distributionof the chemical previous to the drying process Fig; 6 is adiagrammaticsection of the dried embossed material of Fig. 5 wherein thelocalization of the chemical has been indicated; and

Fig. 7 is a perspective view of a roller that may be employed forembossing the fibrous material indicated inFigs. 2 and 3.

Referring now moreparticularly to Fig. 1, wherein one means is showndiagrammatically ousiy rotating drum 15 by virtue of the suctionappliedto the interior of the drum and the sub- The fibrous mat I6 is thencontinuously removed from the. drum, aided by a small roller 11. The matl6, being in the wet condition and containing a substantial proportionof. the soluble migrating chemical, is passed through the felt rollersl8 and IS in order to remove a. proportion of the water solutiontherefrom. The wet mat I8 is then passed between suitable embossingrolls 20 and 2|. The embossing rolls emboss figures of any'desired shapeand size upon the mat l6, such as are indicated in Figs. 2 and 3. Ifdesired, each of the emboss ing rolls 20 and 2| may produce a pattern oneach side of the fibrous mat. The mat I 6, after having been subjectedto the embosslng'treatment, has at least one surface which has aplurality of raised portions 22. The wet embossed mat is then subjectedto a drying treatment in a suitable drying chamber 23. The water withinthe mat evaporates from the surfaces of the board during this treatment,and the migrating chemical concentrates on or adjacent the surfaces fromwhich the water is evaporated. It will be observed (Fig. 6) that thechemical will become more concentrated in those portions 24 of the boardwhich have the raised projections or wicks 22,- since the drying willoccur more rapidly at these points due to the greater surface exposureof that portion of the surface.

The board thus made, having its surface covered with localized areas ofcolor-inducing chemical, is then subjected to heat and pressure in ahydraulic press 25 wherein a finished board of the desired density maybe produced. A break in the sheet is indicated at 25a, at which positiona looper or other device may be positioned for compensating for thecontinuous feeding of the sheet into the discontinuously operatingpress. It is clear that a continuously operating roller press may beused if desired. In order to produce a hard, dense, fibrous board, it ispreferable for making a product in accordance with this invention, a 5%suspension of. fibrous material I I, such as finely comminutedcottonwood fibers,

.is introduced into a suitable tank I! through chloride, is introduceddirectly into the fibrous suspension inany desired amount, such forexample as 1%.

' A fibrous mat i0 is formed. on the continu- 75 of this invention. Suchproducts may not have to employ pressures on the order of about 2500pounds per square inch and temperatures on the press platens of frombetween 350 and 500 F., say about 420 F. The board may be subjected tothis treatment for a total period of from, say, three to ten minutes.The degree or severity of the treatment given to the product,

however, will depend in a large measure on the density desired in theresulting product and the amount of browning or coloration that isdesired. It will be observed that, due to the fact that the chemical, isconcentrated in distinctly different areas of the dried'surface mat,previous to the hot pressing operation, a higher degree of colorationoccurs in those areas. The resulting product consequently has .a.variegated surface which presents a very pleasing appearance.

The completed fiber board produced in accordance with theabove-described method has a. substantially uniform density and issubstantially uniformly porous throughout its entire surface, since ithas been produced from a fibrous mat which was of substantially uniformthickness premoval of portions of the material from various areas of thesurface. A product that is so produced is contemplated as being withinthe'scope In certain inuniform densities and porosities, however,because of the variable amount of material pressed in the variousportions between the press platens. If the product is produced asdescribed hereinabove however, a uniformly dense and porous productresults, since the embossing roll or other pattern-producing means doesnot disturb the amount of material in the various portions of theunpressed board. It is desirable that the surface of the product be ofuniform porosity in order that the product may be readily and evenlypainted without the production of undesired mottled effects on thepainted surface. If the board is not of uniform porosity, it oftenhappens that moisture will be absorbed by the more porous surfaces, thuscausing the board to become wrinkled or warped.

As has been previously indicated, a great variety of color-inducingchemicals may be employed in this process in any suitableconcentrations.

In general, any chemical may be employed which will tend to increase oreven decrease the degree of browning or coloration imparted to thefibrous material during the hot pressing operation. In the method thathas been described hereinabove, it is preferable to use a chemicalthat'is soluble in water in the concentration used or which will migrateto the surface of the board in the manner described above. It may bedesirable in certain instances to use a relatively volatile chemical,such as ammonium carbonate, in order that it will volatilize away fromthe surface of the board when the heat and pressure are removed afterthe pressing treatment. Certain coloredsalts may also be employed, whichwill in themselves lend a color to the resulting product, suitableexamples being a cobalt salt such as the sulfate and a nickel salt suchas the chloride. Other chemicals that have been found satisfactory foruse in practicing this invention are ferric salts, aluminum salts,sulfuric acid, aluminum chloride, oxalic acid, ammonium oxalate,

and the like. If desired, silver nitrate or other photosensitivematerials may be employed.

It is not contemplated'that this invention be restricted to the use ofan embossing roll such as is shown in the above example. Any type ofroll or wet press may be provided which will impart the desired designtothe wet mat. It has also been found practicable to form the matcontaining the chemical and, by means of a suitable mechanism, raiseportions of the formed mat by picking or brushing, preliminary to dryinWicks produced on a wet mat by picking of the fibers from the mat areindicated in Fig. 4. Effectively the same migration of the chemicalduring drying is obtained as if the mat were passed through an embossingroll as previou ly described.

It is also contemplated in this invention that a fiber board havingdifierent colors on each side may be produced without the employment ofplatens heated to different temperatures. Consequently, if a wet matcontaining the chemical is dried from only one side, the chemical willbe- .concentrated on that side and a difierent color will be produced onthat surface when the prodnot is finally pressed. Obviously the chemicalmight be applied to only one side.

It is not contemplated that this invention be restricted to a hard denseboard or method for producing it. The process may be likewise applied toa fibrous mat which is subjected to asufficient temperature and pressureto cause the coloration of the surface but insufiicient to compact theinner portions of the board to a hard dense mass. The process may alsobe applicable to the compaction of heets of undefibrated wood.

The chemical need not be'incorporated and distributed within the mat asdescribed in the above given example. If desired, the chemical may besprinkled or splotched onto the surface of the formed mat in a regularpattern or in a haphazard fashion. If the chemical is applied in thismanner, it may be done at any time prev'ious to the final pressing ofthe board, whether the mat be in the wet or dry condition. In accordancewith one preferred method, the chemi-.

cal may be introduced onto the surface of the freshly formed fibrous matas it emerges from the suspension. The chemical may be here applied inthe form of a spray of solution at a point where suction of therevolving cylinder I5 is still being applied to the mat and the chemicalwill be sucked into the mat and become distributed throughout.

While several particular embodiments of this invention are describedabove, it will be understood, of course, that the invention is not to belimited thereto, since many modifications may be made, and it iscontemplated, therefore, by the appendedclaims, to cover any suchmodifications as fall within the true spirit and scope of thisinvention.

I claim:

1. A process for the production of a hard pressed board which comprisesforming a mat from a suspension of vegetable fibers in an acidic aqueoussolution of a color-inducing compound selected from the group consistingof acid and acidic .metal salts which increase the rate of is depositedadjacent the surface of said mat and concentrated around said portions,and further compacting said mat at a temperature within the range ofabout 350 to about 500 F. in order to form said board, whereby thesurface of said board assumes a color proportional to the amount ofcolor-inducing compound present adjacent said surface. 7 I

2. Process of producing hardboard having a variegated irregularlycolored surface which comprises the steps of mixing a water-solublecolorinducing chemical with an aqueous suspension of woody fibers,forming said suspension into a mat, compacting said mat to squeeze watertherefrom, forming raised portions on a surface of said compacted mat toserve as wicks for se-- lectively drawing the said color-inducingchemical to the raised areas during the drying of said mat, drying saidmat to remove substantially all of the water therefrom whereby saidcolor-inducing chemical is deposited adjacent the surface of" -said matand concentrated around said raised tively drawing the said chemical tothe raised areas duringthe drying or said matrdrying said mat to removesubstantially all or the" water therefrom whereby said chemical isdeposited ad- Jaoent the surface 'ot-sald .mat and concentrated aroundsaid raised portions, and further compactin: said mat by a pressure orat least 500 pounds of said board assumes a color proportional to theamount or color-inducing chemical present adjacent said surface.

HARRY K. LINZELL.

